The goal of this work is to determine the structural organization of the individual globin genes in chromatin. Pancreatic DNAse I is used as a probe of chromatin structure since transcriptionally active genes in isolated nuclei have been shown to be exquisitely sensitive to this enzyme. Prior studies have shown that the gamma globin gene is in the open conformation in fetal erythroid cells from sheep but the adult beta globin genes are insensitive to DNAse I. The adult beta globin genes are activated during the developmental switch but the gamma gene also remains in the active conformation. Maturation of mouse erythroleukemia cells in vitro is also not associated with a major change in globin gene conformation. These studies are being extended to include the DNA sequences around and between the individual globin genes. Cloned DNA segments including mouse, human, and sheep globin genes are sources of probes both for the coding sequences and for the flanking sequences of these genes.